Charge forming device



Nov. 19, 1946. F. c. MocK 2,411,287

`calname FORMING DEVICE Filed Dec. 29, 1941 2 sheets-sheet 1` s Patented Nov. 19, `194,6

@UNITED STATI-:s PATENT. orrlcs y i. 12,411,291"

, CHARGE FoRMnvG DEVICE` e u `Frank c. Mock, south Bend., Ina.,a`ss1g`nor to l. Bendix Aviation Corporation; South Bend, Ind.,

`acorporation of Delaware Application December 29, 1941, serial No. 424315` 11 Claims.

This invention relates to charge forming devices for internal combustion engines, principally of the aircraft" type, and more particularly to mixture controls therefor for modifying or controlling the richnessof the mixture supplied to the engine in response to variations, in the velocityoru density of thejairiiowing through the device.V The instant mixture control is particuc 2 orvelocity of air flow. These assumptions are substantially correct through the relatively low range of air velocities previously experienced in carburetors and as a consequence an altitude mixture control which modified the richness a given percentage in accordance with the altitude would inherently correct the richnesslat all `air larly adapted for use witha charge forming dei vice of the pressurefeed type disclosed in my `co pending U. S. application Serial No. 202,206, illed April 15, 1938, nowPatent` No. 2,390,658v dated Dec. 11, 1945, `is an improvement over the mixture control disclosed therein. e Y

e The recent trend in aircraft enginedesign is toward higher supercharging capacity sothat the full or rated` horsepower of?n the engine may be` deve1oped` up toas great an altitude as possible, a. boost control or other limiting device being used to prevent overcharging the engine at lower altitudes. Since substantially the same weight ofairisfrequired by the engine at rated horsepower regardless 'of altitude, it is apparent that the air velocity through the venturi or other air metering device of the lengine carbuburetor is proportionately increased as the air density decreases so as to supply the required weight of` air.` Thus, if rated horsepoweris, maintained up to an altitude of 20,000 ft., at which theair` density is roughly one-half that at ground level, the air velocity in the venturi will be double the maximum air velocity experiencedon the ground. Similarly, if the rated altitudev is 30,000 ft., the velocity willbenearly three .times that at ground level. Thus, the recent and substantial `increases in rated altitude necessitate that the carburetor operate satisfac torily through a very much higher range of Venturi air velocities than heretofore.`

Considerable diiliculty lhas been experienced in obtaining proper fuel-air proportioning'with such increased air velocities, particularly `be` cause the differential pressure created' bythe venturi increases much more rapidly than desired in the high `velocity range.` It has gen'- erally been assumed that the Venturi differential pressureffor aconstant `entering air density, varies substantially as` the square ofthe velocity of flow, and since fuel flow through an orifice varies in accordance with the same law, substantially constant fuel-air proportioning is obtained. It has further been assumed vthat a change in air density, as with change in altitude, increases theirichness ofthe mixture a fixed percentage throughout the range of weight flows at that altitude.

Ithas been found, however, particularly carl buretors in which the fuel is not injected into the venturi, that the Venturi`depression does not vary as the square of the velocity in the "high velocity ranges now experienced, but rather def parts suddenly and drastically therefrom as the velocitypproaches some high or critical value, and as Va consequence the mixture richness is greatly increased. This effect` is at least partially compensated for in carburetors in which fuel is delivered into the venturi as the `fuel vaporizes" andl tends topartially satisfy or overcome the the excessive suction; however, no such compensation is obtained when the fuel is not delivered into the venturi. Analtitude mixture controlo! conventional constant percentage type, although able to properly compensate the mixturethrough the low range of veloci-ties, `pro`- vides insufficient compensation in the high 1 velocity range.

It is accordingly an object of the present invention to provide a carburetor having an improved altitude ,mixture control of the automatic type. j 1

, Itis a further object of the invention toprovide `a carburetor altitude mixture control capable of automatically correcting therichness of the mixture through wide ranges of air density l variations in the enteringair temperature and pressure, and Venturi air velocity. f r- Other objects andadvantages will` be readily apparent to oneskilled in the art from thelfollowing description'talreninV connection with the accompanying drawin'gsingwhich:

Figure 1 is a dmgrammauclsjecuonal view ory e a carburetor of the pressure feed type embody-` ing the invention;` l

fand a fuel duct I.

Y Figure 2 is a p artlal view in section of a modiy yond that normally experienced in a carburetor.

treme inward movement ofthe valve 84:.LA second tapered valve 89 is operated by the throttle through link and bell crank 1I, and isadapted to variably restrict-the passage 59 as the throtg tle approaches closed position. The double locknut arrangement 12 permits adjustment of the valve 89 relative to the throttle. As shown the With reference yto Figure 1, in which much of the structure is as shown in my said copending application Serial No. 202,206 an air passage 10 leads to a blower or supercharger II of either a single or multi-stage type having adischarge.:

ring I2 in communication with the cylinders of.

an internal combustion engine. 'I'he passage I 9 has an air entrance section I4 which'normally opens in the direction of travel of the craft and the passagek and is operated by a rody I6 extending from the pilots compartment. The pilotv thus directly controls the air charge of the engine while the fuel charge isautomatically controlled by apparatus hereinafter described. Anterior to the throttle is a large venturi 'I8 having an annular chamber I9 which is in communication with the air entrance through a plurality of circumferentially spaced` impact tubes 28. A small venturi 22, positioned within the venturi I8 in the customary manner, includes an chamber 23 `opening substantially into the Venturi throat.4 v y A fuel pump, indicated generally atV 25, is of is referred to as a scoop. A throttle I5 controls the slidingvane type having` a by-passpassage 21 controlled by a spring-loaded valve 28. `'I'he pump receives fuel through a pipe 29 and delivers it through pipe 30 to'an annular Vchamber' 32 of a main fuel regulator indicated at 34. @A vapor venting pipe `leadsback'tofthe fuel supply tankv from the uppermost portion of chamberfd i f and is controlled by a float type valve 38.

vThe fuel regulator 34 comprisesjnve cham# bers 38, 39,40, 4|'and 42 separated from ,each other by two large plate-backed actuating dia-,-

phragms 43 andx'44, andby two small sealing diaphragms 45 and 45. 'I'he diaphragms are each preformed with 'an annular groove adjacent the I y `5o thereof without;v change in effective area.. 'I'he 1 outer periphery. to permit axial displacement diaphragms aresecured to a central control rod 5I) having a spherical guide portion 5I at one end and a slide valve 52 connected thereto at its other end. f The valve 52 controls a 'set of ports 53 between thean'nular chamber 32 andthe unmetered fuel lchamber 38 whereby axial movementof the diaphragm-valve assembly varies the effective area of portsV 53 and the quantity of fuel flowing therethrough. vAn idle spring 54 urges the control rod 5I) and valve 52v in a. direction to maintainV a slight opening of the ports 53.l

-A passage 58Iin the control rod 50 forms a pressure transmitting connection between the chamber 42 and the vunmetered fuel chamber 38. The chamber38 -is' also connected'to the metered fuel vchamber 39 by means of a'fuel duct 58, a

pair of oriilces-59 and 88 in parallel relationship If desired, a calibrated orivalves 64 and 89 cooperate with the opposite ends of a single orifice 59 ;.however,` it will be apparent'that each could cooperate with separate orices in series relationship. The economizer orifice 58 is controlled by a spring closed valve 14 rsecured to a diaphragm 15, one side of which is 4subjected'to the .pressure in the unmetered fuel chamber 38 throughpipe 18, and the other side is subjected to the pressure in the metered fuel chamber 38. A small calibrated vent 11 is 'provided for eliminating air and vvapor to permit a complete fuel filling of the device.

vThe metered fuel chamber' 39 is connected to the induction passage through duct 6I, a pipe 80, and a discharge nozzle 8I having asprlng closed,

an air passage fand is therefore subjected .tol

the pressure existing at the throatfof the` primary venturi.` The chamber 4Iv is connected tothe annular chamberby an air passage 88, ports 81 and 88 and passage 89, and is thereforesub-l jected to the pressure in thefair scoop. A calibrated port interconnectsthe ,Venturi passage 85 and the air chamber 4I.v 4,Port 88is con- Vtrolledby a spring closed valve 92 whichfmay be opened, in case of anemer'geney :to by-pass the port 81, by extremel .movement of link 85by" means of the bell`crank 66, a link 93 and a bellcrank 94 having an overrunninglconnection with the valve-9|. The port'81 is controlled byfa` tapered auto` matic mixture control valve95 connectedto the freeend of a. lsealed capsule 961 mounted `in`, a

chamberf91. AI'he device of`Figure-1 als sof'ar described conformswith the device .shown'in my above-mentioned copending.. application Serial INo. 202,206 however, linthe said appucauontue cham-ber 91 is' infreecommunication Withhe air inlet ywhereas in accordance with .theeinstant invention the chamber communicates with the air inlet I4 through a ycalibrated port 98 and with the Venturi air passage 85 l.through acali bratedport 99. The port 99 is normallylarger than vthe port 98 so that the pressure in chamber 91, although intermediate between, the-yen",-` turi and air scoop pressures, willtendV to more nearly` approach that at the venturi than-that in thelair scoop. However, the relative 4size of the ports 98 and 99 maybe varied to obtain any desired relationbetween the pressurezinV chamber f91 and the pressures inV the venturi and scoopyhoweverl the port 98 maybe omitted if desired and the chamber91 subjected to the; full suction of the venturi. 'I'he continuous flowof air fromlthe scoop. :through port; 98, across the surface of bellows 96 and'out port99 .tendsito make thebellowsguickly responsive to variations n I in the temperature Aof thevair enteringthein duction passage. i r i V,During operation'of the engine, the air .flow through the induction passage creates a differential inthe pressures in theannular vchamber 23 of the venturi 22` and thewannular chamber, I9 which, at least.through-.the low, rangeof velocities in the induction passage, varies substantially as the square of the rate of air flow n therethrough. Thesev pressures, throughpassages 85 and 86 to chambers 40 and y4I, acting on opposite sides of diaphragm 44 l create a force tendingto move the controlrod..` "50 to the rightjtol open valve 52.' If this force was not counteracted, it would completely open valve 52:however, as the valve opens fuel the supplied to pipe 30 by the pump 28 flows into the unmetered fuel chamber 38, through orifices 82 and, into the channel 6l communicating with the metered fuel chamber 3,9, through pipe 80 to the dischargeriozzle 8|, and discharges into the induction passage, The flow of fuel through the orifices 62 and results in a differential in transmitted i the pressures in chambers 38 and 3B `whichvaries substantially as the square of the rate of fuel flow therethrough; These pressures acting on t diaphragm 43 urge kthe rod 5U and valve'52` to the left tending to close the ports 53( The Acontrol rod 50 and valve 52 therefore iloat under the action of the air force on diaphragm 44 and the fuel force on diaphrag'm43, and thereby regulate the quantity of fuel in `accordance `with the quantity of air. Thus, if thelquantity of air increases, the air force on` diaphragm 44 `will increase and will open the valve 52 to increase the fuel ow sufllciently to increase the fuel differ'- K ential pressure and the fuel force on diaphragm 43 lto balance the increased air force.` `Constant fuel airrproportioning will thus be vobtained as long as the fuel and air forces on the diaphragms vary in laccordance with the quantity of air and ffuel flow tothe engine, unless the balance on the controlrod is upset by some extraneous force such as idle spring 54. At idle, the force of spring 54 is an appreciable factor in urging the rod 50 tothe right, and consequently, an increased fuel force isrequired to balance both the `airforce and the spring force thereby creating a rich mixture at idle as desired."` Atrhigher air flowsthe force 'of the idle springfis very small in comparison with the relatively large air force and consequently `has but `a negligible effect on the richness `of the mixture. IIt has been found desirable todesign spring `54 to produce a richer mixture trolled valveV 69 to restrict the fuel orifice 59 at closed throttle to obtain the `desired richness of `1n'ixture.``

. It willbe apparent that the regulator 34 maintains the differential ful"` pressure 'across diaphragm 43 at a value depending upon the air flow, andthat a change in the effective area of the fuel meteringjorice will correspondingly change the richness of the mixture. "I'hus, operation of the link 65 will vary the position of the `tapered valve $4 and will therefore vary the richness of the mixture.`^A manual mixture control is thus provided. `Extreme movement to the left at idle' than desired and tense the throttle con- 'when the economizer valve 14 is open the orifice 82 is the primary metering restriction, at` v which time movement ofthe valve 64 willhave f substantially no 'eiecton therichness of the mixture.` The arrangement ofthe orices 2,59,

j and 60" is the same asis shown in myabovefmentioned copending application.

As is generally` knmwn,A the` venturi-man- `scoop differential fpressure created by a given weight of air owfper minute `will increase with decrease in air density and if applied across the diaphragm 4,4w`illfproduce`an increase in 1the fuel flow and consequently arichermixture. lIt has further been discovered thatas the airvelocity through `the venturi increases-beyond a relatively` high value, 'the Venturi l, differential pressure increases at a ratefconsiderably greater than the square `of the air` velocity, thus vproducing an enrichmentof thelmixture,` at` high air velocities.. 1

The foregoinginherentimetermg characterisf- ,l Atics are clearly shovvnin the graphof Figureiin which the mixture `richness has `been plotted against the weight of air iloivfor various altitudes. The characteristics of -asingle Venturi carburetor` are shown in full lines and those "of a multiple Venturi carburetor in broken lines.

The richness scale` in y Figure 5 jutilizes unity (1.0) todesignate the desired richnessfor operation at ground level, and theweight of air `scale utilizes unity ;(1.0) to designate the maximum weight` of air which `can be drawn through the Venturi system with an entering air density corresponding to yground level', at which timev the air velocity inthe main venturi reaches its maximum or critical value. "The circled termination` point of each of the curves corresponds to critical flow at that particular altitude. It will be noted that themetering characteristics of single or multiple Venturi carburetors are substantially the same through the major portionpi the air flowfrange but sharply divergeasthe maximum flow isapproached. Thisfresultsfrom the fact that the velocity'n the small venturiis greater than that in the main venturi and asa consequence reaches a condition of critical flow. before the main venturi. Atthis time the depression in` the small venturi, which determines the fuel flow, reaches a maximum: and subsequent increase in flow through theflar'ge venturto its critical ilow of link causes thedisc 61 to fully closeorifice' 59 to shutoff thefuel flow` so as to stop the engine.

As the power output from the engine increases A the fuel consumption and consequently the fuel diiferential pressure `across diaphragm 43 and therefore across `diaphragm 15 correspondingly increase.` When the fuel differential pressureV reaches :some predetermined value `the dia" 4phragm 'l5 opens the economizer `valve 14 and thereby increases the richness of the mixture for high power operation, as is desired.` Theorice Slis normally greater` than the effective area `of the orifice 59 but smaller than the sum of the areas of orinces 5S and 60." Asa consequence rate increases the total air iloWwithout increasing thefuel ow. "The mixture richness through this range is therefore decreased as indicated by thebroken lines which diverge from the solid lines. f

It must be borne in mind that these curves ex` tend into regions of velocity far in excess of those previously orl at"`present experienced, or even contemplated, in carburetors forinternal come bustion engines',`-but have been here shown Vmere-` U ly to indicate the full characteristicpf ysuch de-` vices. Up until but a few years ago,few airplanes were able toreachaltitudes above 20,000`ft. and utilized `maximum air flow values roughly indie cated byi the dotted ,line a--bgthe maximum weight of airisupplied to the `engine decreasing with increase in altitude. Through this limited range of altitude and air flow, as determined by the line a-b and ,the ground level and 20,000` ft. s

curves, a carburetor tends to produce a substantially constant richness of mixture `at each altitude. In' order to obtain a mixture richness at altitude equal to thatfat ground level,V the altitude mixture control may apply a percentage correction dependentupon the altitude.`

ntiend ofsuperchargers andI l.iinproved charging of the vengines the maximum air-now ateach altitude was' somewhat increased f` as indicated by the line ced; howeven substan-` tially constant richness is vobtained'at each altitude even throug l i'|:'hisl somewhat enlarged range,

land an altitude control iunctioning solely in re" sponseto variations'in" ent ering. air density satisfactorily compensatesthe richness of the `mixture at various altitudes regardless of. the rate ofair'low.

With proposed highly superchargedand boostaltitude is substantially as de'ned by ythe lline eff.. `Through theI greatly increased velocity lranges now experienced,`particularly at altitude,

the richness nolonger tends to "remain constant Vat each altitude, but rather increases sharply i with the increased `velocity. A naltitude mixture 1 control which at a` given'altitude applies the necessary percentage correction atr low air flows, provides insufiicient compensation at the high air flows.

'To accomplish the desired mixture correction for variations in altitude and' velocity I provide, referring againto Figure l`1, thevalve 95 Afor variably restricting the port 8 1. vWhen the' valve 95 is withdrawn from the port.as'a1` low power.

ground level'operation, thefcalibrated port 98, being o fnfsmall size in comparison with the port 81,' 'has substantiallyno effect on the' pressures in chambers 40 `and 4|. However, movement 'of the valve 95 into a`restricting` position in port 81 restricts the flow of air'` from the annular ,chamber |9 :to thejchaxnber 4 1 and consequently the Venturi suction in passagej 85 is effective to partially reduce the Ypressure in chamber 4| and controlled engines the maximum airflowat each therebydecreases'the differential pressure across Y diaphragm 44. The richness of the mixture is correspondingly decreased. The valve 95`is vari ably positioned within theport 81 by the expansibleI bellows 96. subjectedr to a pressurevarying in accordancewithth'e absolute pressure in a venturi positioned interior to vthe throttle and preferably forming a ,portion of the` tuel metering instrumentality. In thev modiiicatlonofFlgure 1 Athe bellows issubJected to variations in the absolute pressure inthe venturif`23 by means of the port 99 'i/ntercommunicating vthe bellows chamber91 and the'Venturi passage 85. 'I 'he .port 98 from chamber 91 intothe air rinlet provides a continuous flow of air across `thebellows 96 whereby it will quickly respond to changes in f densityl resultingfrom variations in entering air temperature.A The bleed 98 also rserves to partially destroy the suction within chamber 91 whereby any desired correlationmay be 'obtained in the relative responsiveness of the bellows to variations in the air velocity as'reilected in the absolute Venturi pressure and' to enteringair densityasreilected both in 'the pressure at port 9 8as well as the `pressure in lation o'ffthev contour of valve 95 and the pressurey in chamber 91to produce constant fuel air proportioningatone altitude `will produce substantially the same proportionng at all altitudes.V y In the event that thebellows controlled valve 95' jams or sticks `while in al restricting position, the-emergency valve92 may be opened by extreme movement to theright of link 65,v thereby providingan air by-'pass varound', the valve 95 to prevent undueleanness which would otherwise occur upon reduction in altitude or air velocity `after the valve 95 jammed. t

The embodiment of Figure 2 is somewhat simi the' venturi. Corre- Thechamber |91 'lar to that of Figure 1 and differs therefrom prini cipally inthat the bellows chamber 91 communicatesiwith thethroat of the large venturi. I8

by. means ofv` an open-ended tube |.|l| extending into the `venturiin thedir'e'ctionot air now. `A

|02 is provided' in fthe tubev i |0|. Asfbetore, the rchamber91, `c`ommunictes 'l i with the air; inlet through one orvmoreports 98.

"The remaining structure ,disclosed in Figure 2 is similar to that of Figure land has been given calibrated restriction corresponding reference numerals.'` t In Figure 3, corresponding partShaVmE-been given corresponding'referencefnumerals'with the addition` of 100, a large venturi; ||,8, positioned anterior. to .the throttle |l|5, isprovided with two annular chambers. I |9 and |2|, theforme'r communicating with the. inlet throughimpact .tubes |20, and the latter communicating 4withsubstan` tially the throat of the venturi through fa plurality of ports |24. I Annular chambenlnin'the Smau venturi |22 comuniones .with the cnam.- b e'r 48ofjtheregulator through vthe passage |88 and the annular chamber ||9 communicates .with the chamber 4| 0f the regulator through passages |86 and lowsactuated valve |95. l The chamber. |91 enclosing` the bellows |96 is connected yto the ahchamber |2| by a passage |54 and a calibrated .port |55.` Thebellows of Figure 3 is thus sub- Jected to a pressure dependent upon the` absoing impact pressure.

lute pressure .at the large venturi and .the enter- Figure4 disclosesthe induction passageoffa o' single Venturi 'carburetor in which the .venturi is similar in structure to the large venturioiV Figure 3 4and, is formed with annular chambers 9 andv |2| respectively air. impact pressure and the Venturi throat pressure'. The pressure in chamber l| I9 isV transmittedto the regulator chamber 4| through passages |86 and 1|89 and portV |81.. and the pressure in. chamber i 2| is transmitted to. the chamber '40 ofthe regulator through passages- |54 and |51.

municateswith -the, chambery ||9 through passage |41 and restriction |48 and with'the chamber 2| throughport |55 and passage .|54.` f

Although several forms o1'.;the invention have been disclosed, the Vvarious parts of the separate modifications may readily be combined to torni furthermodiflcations, for example, the chamber |91 of Figure 4 may, if desired; be connected tothe 'air inietas in Figures; and 2 rather than to the impact pressure. chamber the modifications of Figuresl. and 2 may utilize impact ,chamber` I9 rathenthan theconnection 9 8 to the air inlet., Manyother'changes may be made in the arrangement of thevarious r`parts e spirit of the invention fromv withoutdepartilg and I- contemplate the use of alllsuch arrange,-

ments falling, within the scope of theappended claims. Portions of the structure disclosedv ibut not clalmedherein are being claimed rin"myV colpending applications Serial No. 202,206, Vfiled and Serial No.v 362,572, -1filed"` Abrir `l5, 1938, October 24, 1940.

i Iclaiili` `1l i "i 1. In a fuel feeding system for air passage, a throttle in meansV in the air passage anterior to the throttle, a main fuel regulator responsive to variations in' the pressure in the Venturi means for variablyA |89 and port v|81 controlled by ithebela passage |41 havingf a calibratedrestriction |48, and is connected tothe subjected to the entering enclosing the ,bellows |199 com?v pas., similarly,

a connectionfromthe bellows chamber 91 to the an engine,y an the air passage, Venturi chamber, a control element actuated bysaid movable wall and operative to control the-rate `of fueldeliveredto the engine byi the regulator vto .thereby control the richness ofithei mixture,

and a passageway connecting the chamber to a low pressure zone in the Venturi means whereby the movable wall yis subjected .to apressure which decreases with increase inl air ,velocity through the Venturi means and alsoawithan increase in altitude, said passagewayhaving an effective cross-sectional area `whichremains constant with variations inthe positionof said control element. 2. In a fuelfeedingsystem for an enginehaving a throttle controlledair passage,` Venturi `means in said passage anterior to the throttle for creating a pair of air pressures the difference Aof which varies with variations in the air flow through the passage, afuel conduit for supplying fuel tothe engine, means in said conduit for creating'a pair of fuel pressures the difference' of which varies with variations in fuel ow through theconduit, a fuel valve in the conduit, diaphragms operatively connected to the valve and responsive to said pairs of' air'and fuel pressures, and an altitude mixture control comprising an air chamber, a sealed capsule l the air chamber having a wall movable in response to variations` in the absolute pressure and temperature of the air in said air chamber, a control element actuated by said wall and operative to vary at least one of the air pressures on said diaphragme,r and a passageway of fixed cross-sectional area during Venturi means. i

sponsive memberz being `located in said second passage so as to be exposedtothe air flowing therethrough, and means responsive to the pressures at spacedpoints in saidlfirst passage for controlling the flow` of fuel to the engine. 1

l, 6. `,In a fuel supply system for an internal com- A bastion engine having an` air conduitl a throttle in said conduit, Venturi means including `at least one venturi in the conduit anterior to the throttle, a fuel regulator having two airchambers,A a first `passageway connectingthe venturito one o'f the `air chambers, a second passageway connecting the other of the airchambers to the air conduit at a point anterior tothe throttle andfspaced from thethroat of said venturi, 'and means responsive to variations in the` differential of the pressures insaidchambers for controlling the Vfuel flow" to .the engine: the combination therewith of an automaticmixture control fori varying the quantity of fuel supplied to the engine by the regu-V lator fcomprising a i variable pressure chamber having a movable Wall responsive to the absolute i `pressure in said variable,` pressure chamber, -a

`valve connected to said wall to be actuated thereby and operative to vary the pressure in one `ci.'

` Venturi means whereby the pressure in said `var- 3. 'I'he invention deilnedin claim 2 comprising in addition a second passageway connecting the air chamber to azone of relatively higher pressure in the air passage anterior to the throttle.

4. In a fuel feeding system for an engine, an air conduit for` supplying air to the engine, a throttle in the conduit, a venturi in the conduit anterior to the throttle, a passage including a restricted portion connecting the venturi adjacent the throatthereof to a point in said conduit anterior to the throttle and spaced from said throat, a valve in saidipassage, an air chamber in fixed and continuously open pressure communication with the venturi during all periods of engine operation, a sealed capsule in said cham-A fber having a wall connected to said valve and ,actuating the fuel control valve.

5. In a fuel feeding system for an internal combustion engine, an air conduit for supplying air to the engine, a throttle in said conduit, a

venturi in said conduit anterior to the throttle,

a first passage including a restricted portion and Y connecting the throat of said venturi to a point in said conduit spacedfrom said throat,` a valve in said passage, a pressure responsive member for operating said valveto vary the air flow through said passage, a second passage interconnecting two spaced points inthe air conduit anterior to the throttle atl which the pressures differ by an amount varying with the velocity of air now through the conduit, said pressure reiable pressure' chamber is decreased with increase in air velocity through the 4air conduit and also with increase in altitude, saidv vlast named passageway remaining open during all periods of engine operation. Y

7. In a charge forming device for an engine, an air passage having an inlet portion, a throttle in said passage, means in the air passage anterior to the throttle` for creating a', pressure' varying with variationsin the rate of air flow through the air passage. a fuel regulator responsive` to variations in said pressurefor variablycontrolling` the fuel flowto the engine, and an automatic Y` mixture control comprising 4 an air chamber, a`

sealed capsule in said chamber having a wall mov,-

' able in response to variations in the .absolute pressure in said chamber,4 a control element actuated lator to thereby control theratio of fuel and `air l supplied the engine, and a; passageway leading from the chamber and opening into the air passage anterior to the throttle at a point at which the pressure is less than'the pressure in' said inlet portion by an amount which increases 'with increase in the velocity of air flow through the air passage, the cross-sectional area of said passageway remaining nxed with variations in the position of said control element.` e

8. In a charge forming device for an engine, an air passage having an inlet portion. a throttle in the passage, Venturi means including at least one venturi in the passage anterior to the throttle,

a fuel regulator responsive to variations in the l pressure in saidventuri for variably `controlling the fuel flow to the engine in response to variations in the air flow through the air passage, and a mixture control comprising a, chamber having a wall movable in response to variations in the absolute pressure in said chamber, a control element actuated by said movable wall and operative to control the rate of fuel supplied to the en gine to thereby control the richness of the fuel-air mixture. and a pair of passageways of fixed effective cross-sectional area during periods of engine i operation connecting the chamber to the Venturi means and to the said inlet portion, whereby the g movablewall is to variably control the air passaseand also withincrease inv altitude/ l booster kVenturi means into the main' venturi, a main fuel regulator responsiveV to variations inA pressure in the booster Venturi means for variably controlling the fuelilow/to the en-i sine. and anautornaticA mixture controlicompris-v ing a chamber, a pressure transmitting connection 10. In a fuel feedinl system, an airpassauzehavsaid wall and operative afpressure whiclizdes I ycreasesgwith increase in air. velocitythroughy the vI?2.4113375 i,

in: an'inlet, a throttle-in the a malnventuri in the passage anterior. to the throttle, a

l; 9..,In` aA charge forming device for anensine, l e, vathrottlein'the' passage, a main', venturi-in the me anterior tothe throttle,

small venturi discharzingintosaid large venturi,V fuel regulating xnealisv responsive to the pressure in theairV inlet 'andtcrthe4 pressure in the small venturi for controlling the supply of fuel 'to the engine, and an automatic mixture controlcomprising a 'chamber having a wall movablefln respense' to the absolute pressurein said chamber,

a. control-element actuated by said movablewall andv operative to control the rate of fuel delivered tothe engine lto thereby control the richness' `of the mixture, andapassageway connecting the chamber to the small venturi; said passageway Y beingof nxed cross-sectional area. regardless of thepositionofsaid control" element.

vv11. The linvention' dened in c1aim.10 compris` ing` in laddition apassageway 'connecting' the chamber toa point in the air passage anterior -to the throttle and spaced from the small venturi.' I I C. MQCK. 

